1. Field of the Invention
The present invention relates to an optical member having an antireflection property and an optical system using the same, and more particularly, to an optical member suitable for obtaining a high antireflection property in a visible region to a near infrared region over a long period of time, and an optical system using the same.
2. Description of the Related Art
It is known that an antireflection structure using a fine periodic structure having a wavelength of the visible light region or a shorter wavelength forms a fine periodic structure having an appropriate pitch and height, and thereby shows an excellent antireflection property in a wide wavelength region. As a method for forming a fine periodic structure, coating of a film in which fine particles having a particle diameter equal to or less than the wavelength are dispersed (Japanese Patent No. 03,135,944) or the like is known.
Further, it is known that a method of forming a fine periodic structure by formation of a pattern by a finely processing apparatus (electron beam lithography apparatus, laser interference light exposure apparatus, semiconductor light exposure apparatus, etching apparatus, etc.) allows a pitch and a height to be controlled, and enables the formation of the fine periodic structure having an excellent antireflection property (Japanese Patent Application Laid-Open No. S50-70040).
As methods other than the methods described above, methods of growing boehmite that is an oxide hydroxide of aluminum on a substrate to obtain an antireflection effect are known. In those methods, a layer of aluminum oxide (alumina) formed by the vacuum film formation process (Japanese Patent Publication No. S61-48124) or the liquid phase process (sol-gel process) (Japanese Patent Application Laid-Open No. H09-202649) is subjected to water vapor treatment or hot water dipping treatment to form a surface layer into boehmite to form a fine periodic structure, and thereby an antireflection film is obtained.
Further, an antireflection film in which a film which contains SiO2 as a main component and has a refractive index between that of a substrate and that of boehmite is provided between the substrate and the boehmite has been proposed (Japanese Patent Application Laid-Open No. 2006-259711).